"Jarawa!" The cry goes up from the front of the bus and, in an instant, the tourists are on their feet, craning their necks to see a small boy clutching a short spear.

He is standing on the edge of the jungle, watching the convoy of vehicles thunder past on the Andaman trunk road. The tourists lurch towards the right-hand side of the vehicle to catch one last glimpse of him and then the government-run bus is past and he is gone.

The spectacle of more than a third of a million people pouring through the dwindling tribe's jungle reserve each year, many of them intent on catching a glimpse of its largely reclusive inhabitants, prompted an outpouring of fury that could not be ignored.

The Indian government moved swiftly to introduce laws punishing interference with the Jarawa with seven years in jail. Two policemen were arrested over the video, and the inspector general of police was transferred after he was caught taking his family on a human safari. In July the country's supreme court – which ordered the closure of the road in 2002 – banned commercial and tourist activity inside a 5km buffer zone around the tribal reserve, warning that any breach of the order would amount to contempt of court. That should have been the end of the human safaris, the term coined to describe the eight daily convoys of vehicles that run up and down the road through the heart of the pristine jungle.

Last week, however, when the Observer returned to the Andamans, it was business as usual for the human safari industry. Not only does it continue, but it does so with the blessing of the Andaman and Nicobar administration, which runs its own daily tourist bus through the reserve. It costs 1,000 rupees (£11.36) for a ticket on the air-conditioned bus (850 rupees without air conditioning), ostensibly to visit a limestone cave and mud "volcano" on Baratang island, which lies 100km north of the capital, Port Blair – and inside the buffer zone fixed by the supreme court.

Hundreds of private tour operators offer their own versions of the tour. But as the reactions of the bus passengers testify, the real attraction of the trip is that it runs through the Jarawa reserve on South Andaman island and offers the opportunity to see the inhabitants in their natural habitat.

The white bus, with the national tourism advertising slogan "Incredible !ndia" painted on its side in large blue letters, picks up its first passengers next to the statue of Gandhi in the centre of Port Blair at 6.30am. A private bus company offering the same trip is collecting passengers from the same spot. It has been raining heavily, but it starts to ease as the bus heads north, entering the tall forest with its mix of hardwood trees and coconut palms. The bus draws up at the last checkpoint before the reserve to await the start of the second convoy of the day. The 13 passengers climb out and head for the stalls selling snacks and drinks.

Half a dozen cars are parked at the side of the road, also waiting for the convoy to start. Five minutes before the tour is due to depart, a loudspeaker crackles into life, instructing those waiting by their vehicles to stick to the rules, which are set out on the board – not yet updated –next to the police post: don't give the Jarawa bananas and biscuits, don't take pictures, don't stop, don't let the Jarawa into your vehicles. Anyone breaking the law faces five years in jail.

The passengers board the bus and a policeman with a luxuriant handlebar moustache joins the tour, clutching an ancient Lee-Enfield .303 rifle. Then the convoy is off, picking up speed and bouncing along the uneven surface. The rain has stopped and the trees glisten with moisture. Those on board do not have to wait long.

"Jarawa!" The driver points to the side of the road ahead. The tourists are on their feet, eager to catch a glimpse. A man is crouching by the road with a bow on his knees. The bus flashes past. "Jarawa," the tourists say contentedly to each other as they sit down. This is what they came for. The cave is an unimpressive gash in a limestone cliff, the mud "volcano" merely a large puddle that occasionally belches out a few bubbles of gas from decomposing vegetation trapped below. This is the main event. But they have heeded the warnings: no one tries to take pictures and the sealed bus windows make throwing out food an impossibility.

The bus breaks down and everyone is decanted on to the private vehicle that is following behind. There is another hiatus as the convoy squeezes past another, larger one, coming in the opposite direction. Then it is off again, moving swiftly, the new vehicle bouncing fiercely.

"Jarawa!" This time it is two women, naked from the waist up, with bright red cloth wrapped around their heads. The tourists are on their feet.

"Jarawa!" Every few minutes, the cry goes up. Each time the tourists spring up, but there are several false alarms.

The policeman, also standing now, forgets his rifle, propped against the back of a seat, and it crashes to the floor of the bus as the vehicle hits another pothole. He picks it up, glances sideways, then stares straight ahead.

There are 22 people on the bus now and most are on their feet, peering out of the windows on the left side. Then the forest ends abruptly and the bus pulls up next to a jetty. The passengers board a ferry and a local bus and a couple of cars squeeze in behind them. It takes less than 10 minutes to reach Baratang, where a small flotilla of motorboats is waiting to convey the tourists to the walkway that gives way to a muddy path leading 1.2km inland to the cave. A few people make appreciative noises as the guide points out the stalagmites and stalactites inside.

Although Baratang lies within the buffer zone, the island's administration has allowed the tours to continue, claiming that it has sought an eight-week stay to allow time for an appeal, a request refused by the supreme court.

Two boat rides later and the tourists are back on the bus. A couple ask about the "volcano", but the guide shrugs and says it is not worth seeing. At 3pm the convoy sets off, and for those hoping to see members of the tribe it is a vintage afternoon. "Jarawa!" "Jarawa!" "Jarawa!" A woman, then a man, then the child with his spear, then another woman. The tourists are leaning forward, some not even bothering to sit down as they try to get a better view through the windscreen.

This is not a big convoy: a dozen cars, four buses and a couple of lorries. Even so, the vehicles are carrying about 100 people. Another convoy squeezes past, heading towards Baratang, the last northbound convoy of the day, made up of 10 cars and five buses. At the height of the tourist season there can be as many as 150 private tour vehicles on the first convoy of the day alone, along with the tour buses and commercial vehicles. During the tourist season, which runs from September to May, an estimated 250 vehicles use the road each day. The number drops to 150 during the off season.

Even using the low vehicle and passenger figures from this one trip, that amounts to almost 150,000 people a year going up and down the road. Factor in the much higher numbers travelling when the tourist season is at its peak and a very conservative average of 500 people on the road every day produces an annual total of 180,000 people. Even if only half of them were tourists, they outnumber the Jarawa by 228 to one.

There is widespread agreement that this volume of interference with the Jarawa's nomadic, largely insular existence can only hasten their demise.

The Andamans lie in the Bay of Bengal, closer to Burma than to India, and anthropologists say the tribe has been there for tens of thousands of years, probably having migrated from Africa. It is only 14 years since they dropped their hostile attitude towards outsiders and started to come out of the jungle in any numbers. Before that, intruders had to risk attack from members armed with bows and arrows and there were numerous fatal clashes. Some younger members of the tribe are voluntarily seeking contact now, but most shun it.

Environmental groups, including Survival International, warn that interaction with outsiders will lead to destruction of the Jarawa, as it has done with other tribes on the islands, including the Great Andamanese, who once lived in large numbers around Port Blair. Survival has repeatedly called for closure of the road, but the islands' administration appears determined to keep it open to provide access for settlers. It is 10 years since India's supreme court first ordered the closure of the road to protect the Jarawa.

Despite the international outrage, despite the anger of the government in Delhi, despite the rulings of the highest court in the land, despite the repeated interventions of Congress party leader Sonia Gandhi on behalf of the Jarawa, the human safaris go on.